Such diamines have great importance due to the chemical properties resulting from their two terminal amino groups. They are required, inter alia, for the preparation of plastics, e.g. polyamides and specific alkyd resins, and for the production of fabric finishes and adhesives. Condensation of diamines with dicarboxylic acids is used to obtain wetting agents and emulsifiers which are especially useful in the oil industry. Diamines are, moreover, particularly suitable as hardeners in epoxy resins.
These .alpha.,.omega.-diamines can be prepared by various methods; for example, by reduction of dinitriles. However, it has to be borne in mind that the dinitriles required as starting materials are not readily available, but rather can be obtained only by a synthesis involving many steps. For this reason, this method is not commercially important.
If cyclic olefins, for example cyclohexene, are treated with ozone, the corresponding ozonides are obtained, which can be converted into the corresponding diamines by reductive amination. U.S. Pat. No. 2,657,240 describes a process of this type. The yield of diamine which is achievable is only about 30% relative to the cyclohexene used. Transfer of this process to the industrial scale is limited, not only due to the complex preparation and difficult handling of ozone, but also due to the low yield.
German Offenlegungsschrift 2,824,423 describes a two-step process for the preparation of diamines by the reaction of dialdehydes with a monoamine and subsequent treatment of the reaction product with ammonia and hydrogen in the presence of a hydrogenation catalyst. In order to achieve yields which allow the commercial use of the process, it is, however, necessary to use the monoamine in large excess in relation to the dialdehyde.
German Offenlegungsschrift 2,647,317 relates to a two-step process for the preparation of .alpha.,.omega.-diamines by reductive amination of the corresponding dialdehydes. In a first step, the dialdehyde is reacted with ammonia at a low temperature in the presence of a mixture comprising water and an organic solvent, a diimine being formed from the dialdehyde with the elimination of water. This diimine is reacted in a second step by catalytic reduction to form the .alpha.,.omega.-diamine. The .alpha.,.omega.-diamine yield achievable is dependent to a large extent on the temperature used in the preparation of the diimine. The lower this temperature, the higher the yield. Temperatures in the range of -5.degree. to -10.degree. C. produce yields of between about 80 to 90% based on the dialdehyde. If the temperature of diimine formation is increased even slightly (for example to +5.degree. C.), the .alpha.,.omega.-diamine yield is greatly reduced and the formation of undesired by-products increases sharply. The low temperature which is necessary for diimine formation precludes the use of this process; industrially, low temperatures of this type can only be achieved at great cost.